Echocardiographic

Diagnosis

of Cardiac

Allograft

Rejection

Daphne T. Hsu and Henry M. Spotnitz ARDIAC transplantation is accepted therapy for the treatment of end-stage congestive heart failure, but rejection of the cardiac allograft is a limiting factor in long-term survival.’ The early treatment of rejection is essential to the preservation of allograft function. The addition of cyclosporine to the immunosuppressive protocol of prednisone and azathioprine made clinical and laboratory findings unreliable in the early detection of allograft rejection.2 According to present views, immunosuppressivetherapy can be reliably directed only by histological changes seenon endomyocardial biopsy.3*4 Although endomyocardial biopsy has proven invaluable for the detection of allograft rejection, it is an invasive and potentially dangerous procedure. Complications following biopsy include arrhythmias, pneumothorax, ventricular perforation, air embolus,5,6and coronary fistulae.7 In addition, biopsy is uncomfortable for the patient and necessitates repeated radiation exposure. The search for a noninvasive correlate to endomyocardial biopsy has included electrocardiographic,8’9echocardiographic,““’ nuclear cardiographic,12 and magnetic resonance imaging/ spectrographic techniques.13*14 Echocardiographic methods for detection of allograft rejection might provide advantages relative to frequency of study, patient risk and discomfort, and rapidity of data analysis.

C

ENDOMYOCARDIAL BIOPSY-DETECTION ACUTE REJECTION

OF

Cardiac allograft rejection is a graded pathological diagnosismade by endomyocardial biopsy that manifests a spectrum of clinical findings in the heart transplant recipient. The pathological changes seen in the cardiac allograft during acute rejection range from a mononuclear cell infiltrate, with or without associated interstitial edema, to myocyte necrosis, hemorrhage, and interstitial fibrosis.” Prior to the useof cyclosporine, early acute rejection was diagnosed by an S3 and/or S4 gallop rhythm, and/or decreased voltage on electrocardiogram.8 Histologically diagnosed rejection episodes were hemodynamitally more severe and carried a high mortality.3 Following the advent of cyclosporine, the clinical Progress in Cardiovascular

Diseases,

Vol XXXIII,

No 3 (November/December),

presentation of acute rejection was greatly attenuated, and histologic changesin the endomyocardial biopsy were found to precede clinical deterioration and electrocardiographic changes. As a result, frequent endomyocardial biopsiesin cyclosporine-treated heart transplant patients became routine.3%4’16”7 Immunosuppressivetherapy is continuing to evolve and recent innovations include the prophylactic use of OKT-3 monoclonal antibody.17” The impact of immunosuppressive therapy on the useof endomyocardial biopsy and other clinical indices of rejection requires ongoing study. Observations based on echocardiography illustrated in the following section suggest that clinically significant rejection may occur prior to detection by biopsy and that rejection episodesof this type can be difficult to control. OVERVIEW-ECHOCARDIOGRAPHIC APPROACHES TO REJECTION

A variety of echocardiographic techniqueshave been used to characterize the transplanted heart from both an anatomic and functional standpoint. Anatomic changes in the cardiac allograft can be qualitative, eg, size of pericardial effusionsi8 or quantitative (left ventricular (LV) mass, tissue characterization). Quantitative changes frequently reflect histological findings on endomyocardial biopsy, specifically edema, infiltrates, and necrosis. Quantitative studies of rejection have included serial M-mode and twodimensional measurement of left and right ventricular dimensions, as well as left ventricular septal and posterior wall thicknesses. LV mass changes have been derived from M-mode and two-dimensional echocardiographic views, and quantitative parameters have been compared with biopsy data. Echocardiography has also been used to study the systolic and diastolic function of the trans-

From the Departments of Pediatrics bia-presbyterian Medical Center, New Supported in part by USPHS Grant Address reprint requests to Daphne vascular Surgery Research Laboratory, New York, NY 10032. o I990 by W.3. Saunders Company. 0033-0620/90/3303-0002$5.00/O 1990:

pp 149-

160

and Surgery, ColumYork, NY. No. HL-22894. T. Hsu, MD, Cardio630 W 168th St,

149

HSU

planted heart. Myocardial edema alone may decrease LV compliance and echocardiographitally determined isovolumic relaxation time and diastolic mitral flow indices reflect decreased compliance. Systolic function, evaluated qualitatively by regional wall motion abnormalities and quantitatively as fractional shortening and/or ejection fraction, has been useful in acute rejection primarily in evaluating efficacy of therapy rather than as a diagnostic method. Finally, echogenicity of the myocardium would be expected to increase during acute rejection due to edema, lymphocytic infiltration, and necrosis. Consistent with this, ultrasound tissue characterization of the myocardium has also shown promise as a diagnostic tool. VENTRICULAR

MASS DURING

Mass Increases Models

AND

ACUTE

VOLUME

CHANGES

REJECTION

During Rejection-Animal

Acute cardiac rejection, in its early stages, is associated with interstitial edema and diffuse lymphocytic infiltration. These histological changes should be accompanied by an increase in LV mass. Indeed, Nowygrod et al, using heterotopic rat allografts without immunosuppression, demonstrated a progressive increase in allograft weight 3 to 13 days following transplantation.” Administration of lymphocyte globulin immunosuppression delayed the onset of mass increase to post-operative day 9. Scott et al performed heterotopic allograft heart transplantations without immunosuppression in dogs and compared the myocardial wet to dry weight ratios of serial myocardial biopsies with a histopathological score of rejection. 2oThey found that myocardial water content increased over time and correlated significantly with severity of the histopathological score. With cyclosporine immunosuppression, histological evidence of myocardial edema is less prominent than that seen in recipients receiving prednisone and azathioprine alone. Nevertheless, Sadeghi et al demonstrated increased heart mass in cyclosporine-treated rat allografts.21 Statistically significant increases in heart weight were also observed in cyclosporine-treated isografts, suggesting a rejection-independent effect of cyclosporine alone. The mass increases were associated with an increase in myocardial water con-

AND

SPOTNITZ

tent from 75% to 83%, which, as explained below, is sufficient to account quantitatively for the mass changes observed. Quantitative Echocardiographic Studies-Techniques Quantitative echocardiography is a powerful tool but is affected by imaging and planimetry techniques. Accordingly, strict attention must be paid to detail during the acquisition and analysis of the echocardiographic views for quantitation. Image quality must be excellent, and serial studies in the same patient should be obtained by a single echocardiographer using consistent technique and equipment. Planimetry of serial studies should also be performed by a single, highly trained individual. Experience in our laboratory indicates that 6 months of training is required to produce consistent results, although recent improvements in echo quality have reduced the difficulty of training. Although different absolute values may be obtained when data are analyzed by different observers, correlation coefficients are high, so that serial studies analyzed by independent observers show the same trends. Improvements in image quality have not only facilitated planimetry but have also markedly reduced data scatter, making it difficult to determine whether differences between current and earlier studies reflect real clinical differences or simply improved echocardiographic data. Quantitative echocardiography is useful to characterize serial changes in the cardiac allagraft, but it is a time- and labor-intensive process that cannot be supported by current clinical reimbursement rates unless fully automated data analysis becomes feasible. Echocardiographic Models

LV Mass-Mathematical

M-mode echocardiography directly measures variation in thickness of ventricular walls over time, whereas two-dimensional echocardiography measures variation in areas over time. As illustrated in Fig 1, conversion of these data to ventricular mass using mathematical models is essential to avoid errors due to the effects of ventricular volume on wall thickness. M-mode. M-mode determination of LV mass usually assumes the ventricle to be an ellipsoid of revolution in which the minor semiaxes are

ECHOCARDIOGRAPHIC

DIAGNOSIS

OF REJECTION

151

1.6-,

0.2 0.0

1 I I . 0

I *

,

. I c I

50

100 End-Diastolic

I

I

.

1 - *

150

200

Volume

(cc)

8 - I

250

- - 8 1

300

Relation of wall thickness and chamber volume Fig 1. calculated for spherical LV models of 100. 150, and 200 g mass. Wall thickness decreases as end-diastolic volume increases, so that wall thickness for 100 g model at 70 cc exceeds that of 200 g model at 250 cc. Failure to take such geometric factors into account will lead to major errors if wall thickness alone is used to estimate mass.

identical in length. LV internal dimension and posterior and septal wall thicknesses at the level of the tips of the mitral valve leaflets are used to calculate mass.22 Since LV long axis dimension cannot be directly measured with M-mode echocardiography, the long axis is assumed to be twice the short axis length.23 Two-dimensional. Two-dimensional echocardiographic methods for the determination of LV mass have been based on ellipsoids, cones and truncated cones, and Simpson’s rule methods relatively independent of overall geometry. Twodimensional echocardiograms of single or multiple short axis sections are planimetered to obtain endocardial and epicardial areas. The long axis dimension is measured directly, and epicardial and endocardial volumes are determined by multiplying the appropriate area(s) by the appropriate length(s).24 LV mass is obtained by calculating the difference between the epicardial and endocardial volume. This figure for wall volume may be further modified by multiplication by 1.055, the specific gravity of myocardium. Huge changes in water content are required to change the specific gravity of myocardium, an effect that can be ignored for practical purposes. Echocardiographic Limitations

LV Mass-Validation

and

Wyatt et al, using echocardiograms obtained in anesthetized dogs, compared LV mass quanti-

tied by seven mathematical models to ventricular weight postmortem. 25 The four models that used LV short axis area and long axis length, measurements obtained by two-dimensional echocardiography, correlated most closely with true LV mass (r = .938-.948), perhaps because planimetry of the LV short axis area allows for irregularities of the endocardial outline. Models that calculated mass from M-mode derived measurements of long and short axis dimensions correlated less well (r = .744-.890). Helak and Reichek planimetered two-dimensional echocardiographic sections of postmortem human hearts divided in six to 24 slices. LV section volume was calculated by multiplying the appropriate area by section thickness, with the apical section volume assumed to be ellipsoid.26 LV mass was obtained by multiplying LV volume by 1.055, the specific gravity of the myocardium. The results were compared to reference LV volumes obtained from calibrated photographs of the sections and actual LV weights. Echocardiographic LV volume and mass correlated closely with the reference values (r = .90-.97), but LV cavity volume tended to underestimate absolute cavity volume, and LV mass tended to overestimate true ventricular weight. These discrepancies from absolute LV mass and volume have been attributed to planimetry techniques and the resolution capacity of the echocardiogram. A major source of error in all methods of mass determinations is the measurement of LV long axis dimension. The M-mode method assumes that the ventricular long axis is twice the short axis, which has been shown to be anatomically incorrect in many cases. Although two-dimensional echocardiography allows for direct measurement of the LV long axis, technical difficulties in the visualization of the LV apex can lead to errors in the determination. Quantitative Rejection

M-Mode

Studies-Acute

Echocardiographic evidence of rejection-associated increases in left ventricular mass and volume has been sought in patients immunosuppressed with either prednisone and azathioprine alone, or with these agents in combination with cyclosporine. Initial studies, using quantitative M-mode analysis, measured the thickness of the LV posterior free wall, as an indication of in-

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152

creased ventricular mass secondary to edema or infiltration, and the dimensions of the right ventricle and the anterior-posterior diameter of the heart, as a reflection of changes in ventricular volume. The measurements were then correlated with the clinical and laboratory diagnosis of rejection. Prior to the advent of cyclosporine, increases in these indirect indicators of ventricular mass and volume demonstrated a significant relationship with episodes of clinical rejection.lO~ll However, increases in echocardiographic parameters were less sensitive in detecting mild rejection. Early Studies of LV Mass-Pre-Cyclosporine Era Early serial M-mode determinations of LV mass were performed in patients immunosuppressed with prednisone and azathioprine alone. Sagar et al found that serial M-mode estimates of LV mass increased from baseline during episodes of acute cardiac rejection in 13 cardiac transplant patients. 27 Left ventricular mass increased 139% in those patients who had biopsyproven rejection, and then returned to baseline after the rejection episode was successfully treated. Similarly, Dubroff et al, using a twodimensional quantitative determination of LV mass, found that mass increased in two patients in association with biopsy-proven episodes of rejection. 28 The absolute mass changes were less than 20%. The large quantitative differences between these studies could reflect differences in the M-mode and two-dimensional methods of determining LV mass. Clark et al, in a study of 13 rejection episodes in six patients demonstrated an increase in LV mass from 172 to 181 g when an intervening endomyocardial biopsy showed new evidence of rejection and no change in mass when an intervening biopsy showed no evidence of rejection.2g In a similar study comparing nine transplant patients to five normal volunteers, important limitations of serial quantitative echocardiography were identified.30 The scatter of data in the normal volunteers was so great that the 95% confidence limit for a significant mass change was 18 g. Technical improvements in echo imaging since that time have markedly reduced data scatter in serial studies, but more recent studies of normal volunteers have not been reported.

LVMass-Cyclosporine-Treated

AND

SPOTNITZ

Patients

Histological study of endomyocardial biopsy during rejection episodes demonstrates less myocardial edema in patients immunosuppressed with cyclosporine than in patients receiving prednisone and azathioprine alone. As a result, changes in LV mass with rejection might be expected to be less marked. However, contradictory evidence was reported by Mastropolo et al who studied seven rejection episodes in seven transplanted patients receiving cyclosporine immunosuppression. A statistically significant increase in LV mass from 140 to 152 g was observed when an intervening endomyocardial biopsy showed new evidence of rejection. No change in mass occurred when an intervening biopsy showed resolving rejection or no evidence of rejection. 31 A 10 g increase in LV mass in Mastropolo’s study was associated with evidence of rejection in 78% of concurrent biopsies. In Clark’s study using similar methods in the absence of cyclosporine, a 10 g mass increase was associated with evidence of rejection in only 56% of biopsies. On the other hand, Dawkins et al studied 20 orthotopic cardiac transplant recipients and found a wide variation in M-modedetermined LV mass, which did not reflect the presence of rejection on endomyocardial biopsy.32 The large scatter in successive measurements in this study, amounting to as much as 80% of initially measured LV mass, reflects difficulties with M-mode measurements for studies of this type.” Another important difference in our experience at the Columbia-Presbyterian Medical Center has been an overall tendency for LV mass to decrease during posttransplant hospitalization in patients immunosuppressed without cyclosporine whereas mass tends to increase in patients immunosuppressed with cyclosporine. Antunes et al followed serial LV mass changes over time in 14 cardiac allograft recipients using a two-dimensional echocardiographic method.33 The mean follow-up periods were 2 days, 23 days, and 15 months posttransplantation and a statistically significant 15% increase in LV mass was observed between 2 and 23 days, with no further increase in mass observed at late follow-up. These data indicate that acute rejection can cause echocardiographically detectable increases in LV mass with or without cyclosporine immuno-

ECHOCARDIOGRAPHIC

DIAGNOSIS

OF REJECTION

153

suppression. An example of this is seen in Fig 2. This transplant recipient had a rise in LV mass associated with an episode of biopsy-proven rejection. In spite of increased immunosuppression and a biopsy showing resolving rejection, the mass continued to increase and the patient died suddenly.

LVMass-Etiology Rejection

of Changes During

A significant difficulty with echocardiographic study of LV mass variation following transplantation is that mass is affected by factors other than allograft rejection. For example, hemodilution and ischemic injury have been identified as causes of echocardiographically measurable causes of LV mass increase, and allograft recipients are exposed to both of these influences at the time of transplantation. Accordingly, a decrease in LV mass might be anticipated over the first few days after transplantation, as surgical edema resolves. Consistent with this expectation, Hosenpud et al studied 10 allografts pretransplantation and posttransplantation and found a significant inI”” I

LVM

.,=rl:v ? f ?

l40120loo-

AR

NR

80 -

RR

60

0

5 Days

IO After

15 Transplantation

20

25

30

Fig 2. Variation in mass (LVM), end-diastolic volume (EDV), and ejection fraction (EF) of the LV with time in days after transplantation. Measurements were obtained by quantitative two-dimensional echocardiography in a cardiac altograft recipient immunosuppressed with cyclosporine and prednisone. Endomyocerdial biopsy results were no rejection (NRI, acute rejection (AR), and resolving rejection (RR) at the times indicated by the arrows. This patient died, apparently of ongoing rejection, following the last data presented despite increased immunosuppression on day 22. Progressive increases in LV mass of greater than 25% of initial values occurring within 30 days of transplantation should be attributed to rejection and require close observetion until rejection is confirmed or mass increases have stabilized (see Fig 6).

crease in LV posterior wall thickness and myocardial volume from the precardiectomy values to the initial posttransplantation measurements, with subsequent regression of the increases over time. The changes did not correlate with the presence of rejection. Although allograft rejection can cause an LV mass increase that is presumably edema-mediated, present information cannot exclude the possibility of other causes of LV mass increase after transplantation. These causes might include edema due to cyclosporine itself,21 cyclosporine-induced renal failure, fluid retention due to heart failure or prednisone, or LV hypertrophy. Other possibilities include lymphocytic infiltration in acute rejection or increased connective and fibrous tissue in the myocardium. Differentiation of these issues is difficult. Antunes et a133 were able to exclude a number of possible causes of increased LV mass in their series, including arterial blood pressure, total body weight, and mismatch of donor and recipient body surface area. Factors that were not evaluated include catecholamine stress and cardiac output. A perspective on the possibility of true LV hypertrophy as a mechanism of LV mass increase over 30 days is provided in Table 1 which summarizes the time course of LV mass increase under physiological stress. The experimental stresses and hypertrophic responses reflected in the table are more severe than those recognized to occur in transplant recipients. As a result, hypertrophy cannot be ruled out as the primary cause of the 15% mass increase over 30 days observed by Antunes. Myocardial hypertrophy can develop in response to physiological and hormonal stimuli. In the transplant recipient, systemic hypertension is often a side effect of cyclosporine, as well as an effect of high-dose steroid administration in the early period posttransplantation. Hypertension is well known to increase LV mass35; however, regression of ventricular hypertrophy occurs with treatment of the hypertension.36 In addition, the direct effects of cyclosporine and prednisone on the myocardium have not been well defined. There is evidence that ol-adrenergic stimulation can induce myocyte hypertrophy.37 The transplanted heart is denervated, with a resulting change in the number and responsiveness of sympathetic receptors. The hypersensitiGty of

154

HSU

Table

1. Experimental

Stimulus Normal

Models

of Left

Model

growthe

Ventricular

rats

Newborn

rats

% Increase

LVM

Mechanism

O-21 days 21-150 days

7.1 mg/d 7.1 mgfd

Cell number Call size

Aortic constriction Mild6’ Milde8 Mild6’

Rats Rats Rats

28 days 3 days 7 days

16% LVM 10% wet LVM l %ddryLVM

Hypertrophy Edema Protein

Severe66~68 Exercisee6 Exercise”’

Rats Rats Rats

7-8 days 8 weeks 30 days

Hypertrophy Hypertrophy Hypertrophy

Infarction6’

Rats

3 days

30%-5 1% LVM 22% LVM 12to 17/.un LV wall thickness 29% LVM

Hormonal Growth hormone” Thyroxine”

Rats Rats

Volume

Pigs

5-6 weeks 3 days 4 weeks

46% LVM 18% LVM 104% LVM

Hypertrophy Undefined Hypertrophy

Abbreviation:

load” LVM,

left ventricular

SPOTNITZ

Hypertrophy

Time

Newborn

AND

Hypertrophy

mass.

heart rate response to sympathetic stimulation seen following transplantation may be a reflection of greater sympathetic responsiveness of the myocardium as a whole. If factors independent of rejection produce an obligatory increase in LV mass in the first 30 days after transplantation, as suggested by Antunes et al, the difficulty of differentiating mass increase due to minor episodes of rejection from other causes of mass increase could prove insoluble.

possible common physiological explanation for increased LV mass and decreased LV compliance during rejection. Inconsistency between the evidence of edema on biopsy and by echocardiography could imply fixation artifacts related to osmolarity or other factors, an issue that requires further study.

LV Mass and Function-EfSects

Echocardiographically determined systolic and diastolic function of the cardiac allograft has been studied in order to relate physiological

of Edema

Myocardial water content can be measured by drying myocardial samples to constant weight and expressing percent water as [(wet weight dry weight)/(wet weight)] x 100%. Measured in this way, normal water content is approximately 78% in humans and dogs, increasing to 82% in edematous humans37a and higher than 82% in injured canine hearts. The theoretical relation between changes in water content and changes in LV mass can be calculated by appropriate substitution of variables into the equation for myocardial water content; this relation is presented in Fig 3. The expectation that a 2% to 3% increase in myocardial water content can account for a 10 to 15 g increase in LV mass has been confirmed echocardiographically in dogs on cardiopulmonary bypass38 and by direct measurement in isolated pig hearts3’ Furthermore, as illustrated in Fig 4, LV edema is associated with an obligatory decrease in LV compliance in the isolated swine heart.3g This latter observation provides a

PHYSIOLOGIC

CHANGES

CARDIAC

IN THE

ALLOGRAFT

Systolic Function-Acute

Rejection

70 -30

-20

-10 Water

0

10 Absorbed

20

30

40

50

grams

Fig 3. Relation between percent myocardial water content (WC) and change in LV mass calculated for ID0 g LV and assuming all mass variation is due to water absorption. Calculations are based on the relation WC = [(wet weight) - (dry weight)]/(wet weight) X 100. A 4% increase in water content from a normal of 78% to 82% is associated with a 22 g (22%) increase in mass. The prevalence of variation in water content within this range in the literature suggests that echocardiographically detectable variations in LV mass due to edema should be common in pathophysiological states in humans.

ECHOCARDIOGRAPHIC

DIAGNOSIS

Edema

30 1

0 0

I 20

Control

290g

I 40 Volume

155

OF REJECTION

1 60 - ml

'

' 80

Systolic Function-Clinical

2189

'

Uses

Rapid deterioration of systolic function coincident with an acute rejection episode is an indication of rejection of unusual severity. This fact can be useful either in demonstrating the failure of immunotherapy to halt progression of a rejection episode or in demonstrating successful treatment. A persistent decline in systolic function in spite of intensified immunosuppression indicates the need for more aggressive therapy. Figure 5 illustrates the reversal of rejection-induced depression of shortening fraction by successful immunosuppression. Figure 6 illustrates the course of a fatal rejection episode. Persistent LV mass increase suggested rejection despite two negative endomyocardial biopsies. Acute rejection, once demonstrable by biopsy, was accompanied by a further increase in LV mass, decreased end-diastolic volume, and decreased ejection fraction. The patient expired shortly after the final echo study. In contrast with the acute setting, slow deterioration of fractional shortening over time and the appearance of new wall motion abnormalities has been useful in the detection of coronary artery disease,42 believed to reflect chronic rejection of the allograft.43

' 100

Fig 4. Representative example of effect of an edemarelated mass increase from 218 to 290 g on compliance in isolated pig left ventricle. Edema was induced by hypotonic perfusion under conditions producing no alteration in compliance in control studies. These observations link edema and decreased compliance and provide a common mechanism for reports of increased LV mass and diastolic doppler flow abnormalities observed during allograft rejection in humans.

changes in the graft with the diagnosis of cardiac rejection. Systolic LV function has proven to be an insensitive predictor of cardiac rejection. Stinson et al found that a decrease in cardiac index occurred simultaneously with, or only following the onset of, cardiac rejection.40 Dawkins et al found no correlation of peak velocity of circumferential fiber shortening with rejection41 Others have found that echocardiographic ejection fraction and percent fractional shortening are also maintained despite histologically proven rejection. 4*10,32In addition, interpretation of both fractional shortening by M-mode and twodimensional ejection fraction is confused by abnormal septal motion and septal flattening seen in some patients posttransplantation.

Diastolic Function-Influencing

Factors

LV diastolic function has been studied with increasing interest in heart transplantation recipients. Diastolic function is determined in part by mechanical factors including edema, myocardial fibrosis, pericardial effusions, ventricular interactions, hypertrophy, and arterial pressure. Ventricular relaxation is also an important determinant

60 Fig 5. Similar to Fig 2, data illustrate time course of shortening fraction measured by M-mode echocardiography during immunosuppressive therapy for cardiac allograft rejection. Decrease in shortening fraction is coincident with biopsy demonstrating onset of rejection and reverts toward normal with therapy. Simultaneous two-dimensional echo measurements of LV mass were not obtained: M-mode echo data available to the authors is too unreliable to be used for study of variation in LV mass.

z

50 55

z

45

'5

40

g gj

35

z g 'E Q

25

30

20 15

m 14

, 16

-

, 18

*

44 NR NR I m 20

I 22

Months

44 AR RR ’ I m 24

Post-Transplant

I 26

NR m

NR I 28

m

I 30

8

NR

I 32

* 34

156

HSU

160

1

6 0

+ NR

5

10

+ AR

15

Post-Transplant

20

(cc)

25

Day

Fig 6. Data similar to Fig 2 relating observations and biopsy results. The fraction (EF) was a late observation shortly by death due to rejection despite suppression. These data, like those in potential importance of observations of despite negative endomyocardial biopsy.

quantitative echo decline in ejection and was followed maximum immunoFig 2, illustrate the increasing LV mass

and is dependent on loading conditions, metabolic factors influencing calcium availability, heart rate, and ischemia.44 Cardiac allografts may be exposed to many of these influences. Isovolumic

Relaxation

Time-Definition

The isovolumic relaxation time (IVRT), the interval between aortic valve closure and mitral valve opening, has been useful in the detection of abnormalities of diastolic function. IVRT is determined by timing mitral valve opening by M-mode echocardiography and aortic valve closure by phonocardiography. Its duration depends on the systolic blood pressure, the rate of the LV pressure fall in systole, and the mitral opening pressure.45 The IVRT increases in patients who have systemic hypertension, hypertrophic obstructive cardiomyopathy, coronary artery disease, primary pulmonary hypertension, aortic insufficiency, and aortic stenosis. The IVRT is shortened in patients with congestive cardiomyopathy and mitral stenosis.45’46 IVRT-Acute

SPOTNITZ

histologically demonstrated acute rejection was 87%, with a predictive value of 83%. In a similar study, Valantine et al found IVRT prolongation in transplant recipients relative to normal controls; however, the IVRT decreased in 15 of 17 patients with myocyte necrosis.47’48 In a larger series of 55 transplant recipients, Desruennes et al found that a 20% decrease in IVRT had a sensitivity of 60%, a specificity of 87%, and a positive predictive value of 79%.4g The shortening of the IVRT was attributed to early mitral valve opening, possibly secondary to increased left atria1 pressure. Myocardial edema could produce these effects by decreasing LV compliance, as discussed previously. The sensitivity and predictive value of the IVRT during rejection, approach, but cannot replace, the endomyocardial biopsy in the early diagnosis of acute rejection.

LVM(gm’ ED”

4 NR

AND

Rejection

Dawkins et al found that the IVRT was normal in 20 transplantation recipients not exhibiting myocyte necrosis on biopsy, but decreased significantly with the presence of acute myocyte necrosis.41 The sensitivity of IVRT in detecting

Diastolic

Transmitral

Blood Flow-Definition

LV diastolic function has also been assessed by characterizing the transmitral flow velocity profile (TMFVP) during diastole. The TMFVP is composed of two phases: the first represents early rapid atria1 filling, the second, atria1 contraction. Transmitral flow has been characterized by the filling fraction as well as the flow velocity profile of each phase. Alterations in TMFVP have been demonstrated in patients with hypertrophic cardiomyopathy, aortic stenosis, systemic hypertension, mitral valve disease, and coronary artery disease.50,51’52 The abnormalities observed include decreased early rapid diastolic filling, altered peak flow, and flow profiles. TMFVP has been quantitated using cineangiographic and radionuclide techniques; more recently, doppler echocardiography has been validated as a noninvasive method of obtaining diastolic filling parameters. Diastolic Disease

Transmitral

Blood Flow-Cardiac

Spirit0 et al studied LV diastolic function in 12 normal controls and 25 patients with cardiac abnormalities consisting of subaortic obstruction, coronary artery disease, and aortic valve stenosis.53 TMFVP evaluation by doppler echo and the radionuclide angiographic time-activity curve was similar in 12 of 12 controls and in 2 1 of 25 patients with cardiac disease. Rokey et al

ECHOCARDIOGRAPHIC

DIAGNOSIS

OF REJECTION

demonstrated a good correlation of peak atria1 filling rate by doppler with that determined by cineangiography (r = .87).54

Diastolic Transmitral Rejection

Blood Flow-Acute

Valantine et al studied 22 cardiac allograft recipients serially in conjunction with the endomyocardial biopsy and found that the pressure halftime index, an indication of descent from peak velocity of the early mitral flow phase, was significantly shortened compared to nonrejecting values in 23 of the 34 patients with biopsydiagnosed mild to moderate rejection.48 The peak early TMFVP was also increased when biopsy showed cellular infiltration or myocyte necrosis, but large scatter in the data made the increase in TMFVP meaningful in only 6 of 17 patients with infiltration. Desreunnes et al studied rejection and no rejection transplant recipient groups.4g Peak early TMFVP was unchanged in 25 patients with at least one episode of mild to moderate rejection; however, the pressure halftime index did shorten significantly, returning to baseline after treatment. The 30 patients who had no evidence of rejection had no significant change in this doppler index of TMFVP in three consecutive studies. The sensitivity of pressure halftime was 88% with specificity of 87% for the prediction of rejection. A combination of a 20% shortening of isovolumic relaxation time and a 20% decrease in pressure halftime increased the specificity to 93% with a decrease in the sensitivity to 52%.

Diastolic Function-Prediction Rejection

of Acute

More recently IVRT and TMFVP have been used to screen patients for rejection episodes.55 The criteria used were a 15% shortening of the IVRT or pressurehalftime and a 20% increase in peak mitral flow velocity compared to baseline. Five endomyocardial biopsies were performed solely becauseof abnormal doppler indices, and four of the five indicated rejection.

Diastolic Function-Reflection Compliance

of Ventricular

TMFVP and IVRT can detect changes in LV compliance accompanying rejection, but volume loading and systemic hypertension can also affect

157

both indices.51,56 In addition, becausesynchrony of native and donor atria1 contraction affects TMFVP, measurements should be taken only when the native atria1 beat coincides with donor atria1 systole.57,58 Additional difficulties are presented by the chronic state, where decreasedleft ventricular compliance attributed to fibrosis has been reported. 5gFurthermore, abnormalities of the IVRT and TMFVP due to LV restrictiveconstrictive physiology have been reported 1 to 13 years after allografting and may dilute their value for detection of acute rejection.60 ECHOCARDIOGRAPHIC TISSUE CHARACTERIZATION

Tissue Characterization-Echocardiographic Methods Alterations in echo reflectance can be assessed using digital analysis of signal intensity.61 The acoustical properties evaluated include the gray scale, or brightness of the image, variation of ultrasound intensity with the cardiac contraction, and mean echo intensity. Tissue characterization has been used in animal models to study acute cardiac rejection.

Tissue Characterization-Acute Animal Models

Rejection in

Dawkins et a16’ reported that median echo intensity of the left (r = .61) and right (r = .78) ventricles correlated positively with histologic rejection severity. Wear et al demonstrated a statistically significant increase in gray scale intensity ratio at peak histological severity of rejection in five dog cardiac allografts.63 Chandrasekaran et al measuredintegrated echo intensity of the posterior wall of the LV normalized to a soft tissue phantom in five goat cardiac allografts.64 Echo intensity peaked 3 days after transplantation, then declined, remaining significantly above initial values until demise of the animal. Interstitial edema and a patchy cellular infiltrate were seenin myocardial biopsy on day 3, evolving to extensive cellular infiltration and myocytolysis with no interstitial edema on day 7. The regression of edema was felt to account for the regression of echo intensity. The effects of immunosuppression on tissue characterization have not been described in these animal models. Tissue characterization of the myocardium has

158

HSU

not been applied in human cardiac allograft recipients, but the technique has been used in studies of human myocardial infarction.65 SUMMARY

Current echocardiographic methodsare promising for detection of rejection either as an increase in LV massor a decreasein LV compliance. Both increased massand decreasedcompliance during rejection may be mediated by the common mechanism of edema. Edema will appear specifically as increased wall volume in quantitative echocardiograms and, through decreased LV compliance, will be reflected in doppler-derived indices of diastolic filling. Initial difficulties with quantitative echocardiography related to image quality have largely been resolved. These have been replaced by concern for factors independent of rejection that affect LV mass, including hypertrophy due to hypertension or denervation-induced catecholamine hypersensitivity, and secondary effects of the immunosuppressive agents. An additional difficulty with quantitative echocardiography is that convenience for the patient is offset by the labor-intensive nature of planimetry-based analysis that has not yet been supplanted by fully automated methods. Diastolic function abnormalities within the early months following transplantation are indicators of acute rejection. However, their value in the long-term management of transplantation recipients may be diminished by effects of myocardial fibrosis, hypertension-induced hypertrophy, and accelerated coronary atherosclerosis.

AND

SPOTNITZ

Analysis of echocardiographically derived indices of diastolic function is also a labor-intensive processthat may not be economically feasible in the clinical setting. Echocardiography does have unique advantages for characterizing the functional changes accompanying late-onset chronic rejection. At the present time, echocardiographic techniques cannot replace endomyocardial biopsy; however, echocardiography can be a useful adjunct in the monitoring of patients for acute rejection. Clinical experience has demonstrated that both increased LV massand abnormalities of doppler-derived indices of diastolic function can herald the onset of acute rejection in some patients that may be missed by standard techniques of immunological surveillance. Experience is insufficient to define whether different sensitivities of echo measurementsand endomyocardial biopsy are statistical anomaliesor reflect specific differences in the physiology of rejection. Similarly, it is unclear whether poor clinical results frequently seenin such instancesreflect a fundamental property of the rejection episodeor relatively late detection and treatment. A combined echocardiographic approach that includes measurement of LV mass, ultrasound tissue characterization, and evaluation of diastolic function would lead to further understanding of the interrelationship between the anatomical and physiological changesin the transplanted heart. The applications of echocardiography to the study of the cardiac allograft are multiple, and can be expected to increase as technology continues to improve.

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